RE: Subroutine arguments not right yet

["Jeff Wise" <jwise@...>]

Aaron,

Thanks for your reply.  I would have never deduced that from reading the
documentation.  I think I have risen to my level of incompetence...

After I replied to you last time, I decided that I should interpret the
ellipsis literally.  I put it in dummy2 and dummy2 started displaying the
parameters I was trying to send it.  Now I have to determine how to identify
those parms discretely.  I will try to do this before asking for help!

Thanks again for the assistance.

-----Original Message-----
From: lua-bounces@bazar2.conectiva.com.br
[mailto:lua-bounces@bazar2.conectiva.com.br] On Behalf Of Aaron Brown
Sent: Thursday, September 06, 2007 1:34 PM
To: Lua list
Subject: Re: Subroutine arguments not right yet

Jeff Wise wrote:

> Thank you for your reply.  Unfortunately, I have no clue
> what you are telling me.

There are two issues here.  The main one is how to pass
arguments to a file that is executed after loading it with
loadfile.  Here's how to do it, using what's called a vararg
expression:

-- Beginning of the file 1.lua.
print("1.lua's arguments are:", ...)
-- End of 1.lua.

-- Beginning of the file 2.lua.
-- This is more verbose than normal to make clear what's
-- going on:
local Func, ErrStr = loadfile("1.lua")
if Func then
  Func("grape", "pear")
else
  print("Compilation error: " .. ErrStr)
end
-- End of 2.lua.

Now the command line

  lua 1.lua apple banana

results in

  1.lua's arguments are:  apple   banana

and the command line

  lua 2.lua

results in

  1.lua's arguments are:  grape   pear

For more on vararg expressions, see the manual, particularly

  http://www.lua.org/manual/5.1/manual.html#2.5.9

The other issue is this:

> An examination of "loadfil4" reveals that the last 3
> groups of statements are testing multiple ways to invoke
> "dummy2".  It totally escapes me why there is no output
> from dummy2 on call #2.  This is confusing to me.

Ignoring some details, a function call in Lua takes one of
these three forms:

  form 1: VARIABLE(ARGUMENTS)
  form 2: FUNCTION-CALL(ARGUMENTS)
  form 3: (EXPRESSION)(ARGUMENTS)

(Note that this rule is recursive, in that FUNCTION-CALL
itself must be one of these three.)

Call #1 and call #3 from your previous message are examples
of form 2:

> print("Call # 1 --------------------------------")
> assert(loadfile(pgm))(arg1, arg2)  --(arg1, arg2))

> print("Call # 3 --------------------------------")
> assert(loadfile("C:\\lua\\source\\dummy2.lua"))("apple", "banana")

"assert(loadfile(pgm))" is the FUNCTION-CALL and "arg1,
arg2" is the ARGUMENTS.  The function created by loadfile()
is only called after assert() returns it.

Call #2, on the other hand, just loads a file (converting it
to a function) and asserts that the loadfile succeeded; it
never calls the function returned by loadfile:

> print("Call # 2 --------------------------------")
> assert(loadfile("C:\\lua\\source\\dummy2.lua"))

To call it with no arguments, you'd want:

  assert(loadfile("C:\\lua\\source\\dummy2.lua"))()

For more on this, see the syntax chart in the manual:

  http://www.lua.org/manual/5.1/manual.html#8

Hope that helps,

-- 
Aaron
http://arundelo.com/










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